Analysis of peristaltic reflex in young mdx dystrophic mice

Caveolin and NOS in the Development of Muscular Dystrophy

Caveolin is a structural protein within caveolae that may be involved in transmembrane molecular transport and/or various intercellular interactions within cells. Specific mutations of caveolin-3 in muscle fibers are well known to cause limb-girdle muscular dystrophy. Altered expression of caveolin-3 has also been detected in Duchenne muscular dystrophy, which may be a part of the pathological process leading to muscle weakness. Interestingly, it has been shown that the renovation of nitric oxide synthase (NOS) in sarcolemma with muscular dystrophy could improve muscle health, suggesting that NOS may be involved in the pathology of muscular dystrophy. Here, we summarize the notable function of caveolin and/or NOS in skeletal muscle fibers and discuss their involvement in the pathology as well as possible tactics for the innovative treatment of muscular dystrophies.

Motor dysfunction of the gut in Duchenne muscular dystrophy: A review

BACKGROUND

Duchenne's muscular dystrophy (DMD) is a severe type of hereditary, neuromuscular disorder caused by a mutation in the dystrophin gene resulting in the absence or production of truncated dystrophin protein. Conventionally, clinical descriptions of the disorder focus principally on striated muscle defects; however, DMD manifestations involving gastrointestinal (GI) smooth muscle have been reported, even if not rigorously studied.

PURPOSE

The objective of the present review is to offer a comprehensive perspective on the existing knowledge concerning GI manifestations in DMD, focusing the attention on evidence in DMD patients and mdx mice. This includes an assessment of symptomatology, etiological pathways, and potential corrective approaches. This paper could provide helpful information about DMD gastrointestinal implications that could serve as a valuable orientation for prospective research endeavors in this field. This manuscript emphasizes the effectiveness of mdx mice, a DMD animal model, in unraveling mechanistic insights and exploring the pathological alterations in the GI tract. The gastrointestinal consequences evident in patients with DMD and the mdx mice models are a significant area of focus for researchers. The exploration of this area in depth could facilitate the development of more efficient therapeutic approaches and improve the well-being of individuals impacted by the condition.

Insight into the Role of Gut Microbiota in Duchenne Muscular Dystrophy: An Age-Related Study in Mdx Mice

Dystrophin deficiency alters the sarcolemma structure, leading to muscle dystrophy, muscle disuse, and ultimately death. Beyond limb muscle deficits, patients with Duchenne muscular dystrophy have numerous transit disorders. Many studies have highlighted the strong relationship between gut microbiota and skeletal muscle. The aims of this study were: i) to characterize the gut microbiota composition over time up to 1 year in dystrophin-deficient mdx mice, and ii) to analyze the intestine structure and function and expression of genes linked to bacterial-derived metabolites in ileum, blood, and skeletal muscles to study interorgan interactions. Mdx mice displayed a significant reduction in the overall number of different operational taxonomic units and their abundance (α-diversity). Mdx genotype predicted 20% of β-diversity divergence, with a large taxonomic modification of Actinobacteria, Proteobacteria, Tenericutes, and Deferribacteres phyla and the included genera. Interestingly, mdx intestinal motility and gene expressions of tight junction and Ffar2 receptor were down-regulated in the ileum. Concomitantly, circulating inflammatory markers related to gut microbiota (tumor necrosis factor, IL-6, monocyte chemoattractant protein-1) and muscle inflammation Tlr4/Myd88 pathway (Toll-like receptor 4, which recognizes pathogen-associated molecular patterns) were up-regulated. Finally, in mdx mice, adiponectin was reduced in blood and its receptor modulated in muscles. This study highlights a specific gut microbiota composition and highlights interorgan interactions in mdx physiopathology with gut microbiota as the potential central metabolic organ.

Investigating the Potential for Sulforaphane to Attenuate Gastrointestinal Dysfunction in mdx Dystrophic Mice

Gastrointestinal (GI) dysfunction is an important, yet understudied condition associated with Duchenne muscular dystrophy (DMD), with patients reporting bloating, diarrhea, and general discomfort, contributing to a reduced quality of life. In the mdx mouse, the most commonly used mouse model of DMD, studies have confirmed GI dysfunction (reported as altered contractility and GI transit through the small and large intestine), associated with increased local and systemic inflammation. Sulforaphane (SFN) is a natural isothiocyanate with anti-inflammatory and anti-oxidative properties via its activation of Nrf2 signalling that has been shown to improve aspects of the skeletal muscle pathology in dystrophic mice. Whether SFN can similarly improve GI function in muscular dystrophy was unknown. Video imaging and spatiotemporal mapping to assess gastrointestinal contractions in isolated colon preparations from mdx and C57BL/10 mice revealed that SFN reduced contraction frequency when administered ex vivo, demonstrating its therapeutic potential to improve GI function in DMD. To confirm this in vivo, four-week-old male C57BL/10 and mdx mice received vehicle (2% DMSO/corn oil) or SFN (2 mg/kg in 2% DMSO/corn oil) via daily oral gavage five days/week for 4 weeks. SFN administration reduced fibrosis in the diaphragm of mdx mice but did not affect other pathological markers. Gene and protein analysis revealed no change in Nrf2 protein expression or activation of Nrf2 signalling after SFN administration and oral SFN supplementation did not improve GI function in mdx mice. Although ex vivo studies demonstrate SFN’s therapeutic potential for reducing colon contractions, in vivo studies should investigate higher doses and/or alternate routes of administration to confirm SFN’s potential to improve GI function in DMD.

Spatiotemporal Mapping Reveals Regional Gastrointestinal Dysfunction in mdx Dystrophic Mice Ameliorated by Oral L-arginine Supplementation

Background/Aims

Patients with Duchenne muscular dystrophy exhibit significant, ongoing impairments in gastrointestinal (GI) function likely resulting from dysregulated nitric oxide production. Compounds increasing neuronal nitric oxide synthase expression and/or activity could improve GI dysfunction and enhance quality of life for dystrophic patients. We used video imaging and spatiotemporal mapping to identify GI dysfunction in mdx dystrophic mice and determine whether dietary intervention to enhance nitric oxide could alleviate aberrant colonic activity in muscular dystrophy.

Methods

Four-week-old male C57BL/10 and mdx mice received a specialized diet either with no supplementation (control) or supplemented (1 g/kg/day) with L-alanine, L-arginine, or L-citrulline for 8 weeks. At the conclusion of treatment, mice were sacrificed by cervical dislocation and colon motility examined by spatiotemporal (ST) mapping ex vivo.

Results

ST mapping identified increased contraction number in the mid and distal colon of mdx mice on control and L-alanine supplemented diets relative to C57BL/10 mice (P < 0.05). Administration of either L-arginine or L-citrulline attenuated contraction number in distal colons of mdx mice relative to C57BL/10 mice.

Conclusions

GI dysfunction in Duchenne muscular dystrophy has been sadly neglected as an issue affecting quality of life. ST mapping identified regional GI dysfunction in the mdx dystrophic mouse. Dietary interventions to increase nitric oxide signaling in the GI tract reduced the number of colonic contractions and alleviated colonic constriction at rest. These findings in mdx mice reveal that L-arginine can improve colonic motility and has potential therapeutic relevance for alleviating GI discomfort, improving clinical care, and enhancing quality of life in Duchenne muscular dystrophy.

In vivo neutralization of IL-6 receptors ameliorates gastrointestinal dysfunction in dystrophin-deficient mdx mice

BACKGROUND

Duchenne muscular dystrophy (DMD) is a fatal disease characterized by progressive deterioration and degeneration of striated muscle. A mutation resulting in the loss of dystrophin, a structural protein which protects cells from contraction-induced damage, underlies DMD pathophysiology. Damage to muscle fibers results in chronic inflammation and elevated levels of proinflammatory cytokines such as interleukin-6 (IL-6). However, loss of cellular dystrophin also affects neurons and smooth muscle in the gastrointestinal (GI) tract with complaints such as hypomotility, pseudo-obstruction, and constipation reported in DMD patients.

METHODS

Using dystrophin-deficient mdx mice, studies were carried out to examine colonic morphology and function compared with wild-type mice. Treatment with neutralizing IL-6 receptor antibodies (xIL-6R) and/or the corticotropin-releasing factor (CRF) 2 receptor agonist, urocortin 2 (uro2) was tested to determine if they ameliorated GI dysfunction in mdx mice.

KEY RESULTS

Mdx mice exhibited thickening of colonic smooth muscle layers and delayed stress-induced defecation. In organ bath studies, neurally mediated IL-6-evoked contractions were larger in mdx colons. In vivo treatment of mdx mice with xIL-6R normalized defecation rates and colon lengths. Uro2 treatment did not affect motility or morphology. The potentiated colonic contractile response to IL-6 was attenuated by treatment with xIL-6R.

CONCLUSIONS & INFERENCES

These findings confirm the importance of dystrophin in normal GI function and implicate IL-6 as an important regulator of GI motility in the mdx mouse. Inhibition of IL-6 signaling may offer a potential new therapeutic strategy for treating DMD-associated GI symptoms.

Intestine of dystrophic mice presents enhanced contractile resistance to stretching despite morphological impairment

Protein dystrophin is a component of the dystrophin-associated protein complex, which links the contractile machinery to the plasma membrane and to the extracellular matrix. Its absence leads to a condition known as Duchenne muscular dystrophy (DMD), a disease characterized by progressive skeletal muscle degeneration, motor disability, and early death. In mdx mice, the most common DMD animal model, loss of muscle cells is observed, but the overall disease alterations are less intense than in DMD patients. Alterations in gastrointestinal tissues from DMD patients and mdx mice are not yet completely understood. Thus, we investigated the possible relationships between morphological (light and electron microscopy) and contractile function (by recording the isometric contractile response) with alterations in Ca²⁺ handling in the ileum of mdx mice. We evidenced a 27% reduction in the ileal muscular layer thickness, a partial damage to the mucosal layer, and a partial damage to mitochondria of the intestinal myocytes. Functionally, the ileum from mdx presented an enhanced responsiveness during stretch, a mild impairment in both the electromechanical and pharmacomechanical signaling associated with altered calcium influx-induced contraction, with no alterations in the sarcoplasmic reticulum Ca²⁺ storage (maintenance of the caffeine and thapsigargin-induced contraction) compared with control animals. Thus, it is evidenced that the protein dystrophin plays an important role in the preservation of both the microstructure and ultrastructure of mice intestine, while exerting a minor but important role concerning the intestinal contractile responsiveness and calcium handling.

Roles of M2 and M3 muscarinic receptors in the generation of rhythmic motor activity in mouse small intestine

BACKGROUND

The roles of M2 and M3 muscarinic receptor subtypes in the regulation of gut motor activity were investigated.

METHODS

We simultaneously recorded changes in the intraluminal pressure (IP) and longitudinal tension (LT) in small intestinal segments from M2 or M3 receptor knockout (KO) and wild-type (WT) mice.

KEY RESULTS

In the WT preparations, luminal distension induced a continuous rhythmic contractile activity that was characterized by synchronous rises in IP and LT, occurring periodically at a constant interval. Tetrodotoxin completely abolished the response, whereas atropine either abolished or attenuated it. In the majority of the M2 KO preparations, however, no rhythmic activity was observed in response to the luminal distention, even though networks of enteric neurons and interstitial cells of Cajal (ICC) seemed to be intact. Where rhythmic activity did occur in M2 KO preparations, it was atropine resistant. In the M3 KO preparations, the IP and LT were synchronously changed by the luminal distention, but the changes occurred at irregular intervals. The W/W(v) mutant preparations, which lack ICC in the myenteric plexus (ICC-MY), showed results similar to those of the M3 KO preparations. In some of the M2 /M3 double-KO preparations, rhythmic activity was not observed, but in the others, an atropine-resistant rhythmicity appeared.

CONCLUSIONS & INFERENCES

These results suggest that M2 and M3 muscarinic receptors differentially regulate the intestinal motor activity: M2 receptors play an essential role in the generation of rhythmic motor activity, and M3 receptors have a modulatory role in controlling the periodicity of the rhythmic activity together with the ICC-MY.

Gastric emptying, small intestinal transit and fecal output in dystrophic (mdx) mice

Duchenne muscular dystrophy (DMD), which results from deficiency in dystrophin, a sarcolemma protein of skeletal, cardiac and smooth muscle, is characterized by progressive striated muscle degeneration, but various gastrointestinal clinical manifestations have been observed. The aim was to evaluate the possible impact of the dystrophin loss on the gastrointestinal propulsion in mdx mice (animal model for DMD). The gastric emptying of a carboxymethyl cellulose/phenol red dye non-nutrient meal was not significantly different at 20 min from gavaging between wild-type and mdx mice. The intestinal transit and the fecal output were significantly decreased in mdx versus normal animals, although the length of the intestine was similar in both animals. The present results provide evidence for motor intestinal alterations in mdx mice in in vivo conditions.

Functional activity and expression of inducible nitric oxide synthase (iNOS) in muscle of the isolated distal colon of mdx mice

The inducible isoform of nitric oxide (NO) synthase (iNOS), expressed in endothelium, epithelium, and inflammatory cells, produces a large amount of NO. Previous studies on mouse intestine indicate that a muscular iNOS may have a role in the storage of intraluminal content. In this study we investigated the presence and function of iNOS in the colonic smooth muscle cells of 2- and 12-month-old dystrophic (mdx) mice. By using an in vitro isovolumic technique, and immunohistochemical and Western blot analysis, we demonstrated that iNOS is expressed and active in the smooth muscle cells of normal mouse and defective in young adult (2-month-old) mdx mice. Therefore, an altered activity of the muscle iNOS might explain the motility disorders observed in the colon of mdx mice and, from a clinical point of view, the impairment of intestinal function in dystrophic patients.

The Effect of e-, i-, and n-Nitric Oxide Synthase Inhibition on Colonic Motility in Normal and Muscular Dystrophy (Mdx) Mice

To explore the origin of diarrhea or constipation in human Duchenne muscular dystrophy (DMD), the effect of the inhibition of e- , i-, and n-nitric oxide synthase (NOS) on the motility of proximal and distal segments of colon of muscular dystrophy (mdx) and control mice was studied. The frequency of migrating motor complexes (MMC) was higher in the proximal than in the distal segments in mdx colon (0.56 vs. 0.25 cpm) and in the control colon (0.7 vs. 0.25 cpm), and there was no difference when mdx was compared to control segments. High concentrations of NOS inhibitors, including 1,3-PBIT dihydrobromide (1,3-PBIT) and spermine, inhibited MMC. The dose of spermine required to inhibit MMC was lower for the proximal mdx colon than for the distal mdx or control colon. In the presence of tetrodotoxin, spermine (1 mM) and 1,3-PBIT (5 mM) reduced the magnitude of local, rhythmic contractions (LC) paced by the interstitial cells of Cajal (ICC), but 1,3-PBIT (50 microM) increased their magnitude. There was no difference in the effect of spermine and 1,3-PBIT on the LC between mdx and control colon. The results suggest an inhibition of MMC by high concentrations of e-, i-, and n-NOS inhibitors, modulation of ICC activity by e-NOS, and greater susceptibility of MMC to n-NOS inhibition in the mdx proximal than in the control colon, which is very likely because of a deficit in n-NOS in the mdx smooth muscle affecting the MMC pacemaker. A deficit in the effect of mdx smooth muscle n-NOS on an MMC pacemaker may be the origin of diarrhea or constipation in human DMD.

Duodenal contractile activity in dystrophic (mdx) mice: reduction of nitric oxide influence

The present study was undertaken to analyse duodenal contractility in adult dystrophic (mdx) mice. The spontaneous changes of the isometric tension and the responses of longitudinal duodenal muscle to nonadrenergic, noncholinergic (NANC) nerve stimulation and to exogenous drugs were compared between normal and mdx mice. Duodenal segments from mdx mice displayed spontaneous contractions with higher frequency than normals. N omega-nitro-L-arginine methyl ester (L-NAME) increased the frequency of contractions in normals without affecting that in mdx mice. In normals, NANC nerve stimulation elicited a transient relaxation abolished by L-NAME. In mdx mice a frank relaxation was not observed, the inhibitory response consisted just in the suppression of the phasic activity. This response was reduced by L-NAME and abolished by the subsequent addition of alpha-chymotrypsin. In normals, alpha-chymotrypsin hardly affected NANC relaxation, whilst it significantly antagonised that in mdx mice. Mdx duodenal muscle also showed a reduced responsiveness to sodium nitroprusside, and to 8-bromoguanosine 3', 5'-cyclic monophosphate in comparison with normal preparations. The results indicate that mdx mice experience duodenal contractile disturbances due to an impairment of NO function with defective responsiveness of the muscle to NO. The reduction in NO influence is functionally compensated by the peptidergic system.

Synaptic vesicle morphology and recycling are altered in myenteric neurons of mice lacking dystrophin (mdx mice)

Several dystrophin isoforms are known. The full-length isoform is present in striated and smooth muscles and neurons and its lack causes Duchenne Muscular Dystrophy, a progressive myopathy accompanied by mild cognitive deficits and gastrointestinal dismotility. An ultrastructural study was undertaken in the colon of mice lacking full-length dystrophin and maintaining shorter isoforms (mdx mice) to ascertain whether myenteric neurons have an altered morphology. Results showed a significant increase in the size of synaptic vesicle and in the number of recycling vesicles. An enlargement of endoplasmic reticulum cisternae in a subpopulation of neurons was also seen. Immunohistochemistry confirmed that the shorter isoforms were expressed in mdx mice myenteric neurons. These findings indicate the presence of a neuropathy at the myenteric plexus which might justify the defective neuronal control of gastrointestinal motility reported for these animals and which might be correlated with full-length dystrophin loss, since the shorter isoforms are present.

Motility in the isolated mouse colon: migrating motor complexes, myoelectric complexes and pressure waves

This study has used mechanical, together with pressure/volume recordings or electrophysiological recordings, to investigate the spontaneous activity in isolated preparations of mouse colon. In the former preparations, when not distended with fluid, spontaneous colonic migrating motor complexes (CMMCs) were observed using isotonic transducers. When the colons were distended with fluid, CMMCs continued at an increased frequency and in addition were associated temporally, with rises in intraluminal pressure and pulses of distally ejected fluid. 5-Hydroxytryptamine (1 micro mol L-1) or NG-nitro-l-arginine (100 micro mol L-1) increased the frequency of propulsive activity and this activity was abolished by hexamethonium (500 micro mol L-1). In a second preparation, myoelectric complexes recorded from circular muscle cells in colons using intracellular microelectrodes, were found to correlate in frequency and phase with CMMCs. The experiments indicate that CMMCs are intimately related to pressure waves in the fluid-filled viscus and the muscle membrane potential changes that have been recorded during myoelectric complexes are likely to be analogous to those occurring during fluid-filled propulsive activity.

Murine intestinal migrating motor complexes: longitudinal components

Spontaneous migrating contractions have been described in the circular muscle of the isolated mouse colon and terminal ileum, however, spontaneous events equivalent to these have not been reported in the longitudinal muscle. The longitudinal muscle shortenings in the colon and ileum, which are of similar form, frequency and pharmacology to the circular muscle colonic and ileal migrating motor complexes (CMMCs and IMMCs), are recorded in the present study. The spontaneous ileal and colonic longitudinal muscle shortenings appear to be neurally organized as they are abolished by tetrodotoxin (1 micro mol L-1), hexamethonium (500 micro mol L-1) and morphine (1 micro mol L-1). Endogenously released nitric oxide slowed the frequency of spontaneous ileal and colonic longitudinal muscle shortenings and 5-hydroxytryptamine increased their frequency. Hyoscine (1 micro mol L-1) abolished longitudinal shortenings in the ileum and reduced the amplitude of longitudinal shortening by approximately 44% in the colon. Shortenings were effectively abolished by nifedipine (1 micro mol L-1). Surgical sectioning of the colon identified that each region of the colon contracted longitudinally in an independent fashion; the distal colon contracted to the greatest amplitude and lowest frequency. The longitudinal preparation is suitable to initially assess the actions of novel pharmacological agents on spontaneous, neurally coordinated, CMMCs and IMMCs in emptied isolated murine intestines.

Myogenic NOS and endogenous NO production are defective in colon from dystrophic (mdx) mice

The aim of the present study was to evaluate whether alterations in the distribution and/or function of nitric oxide synthase (NOS) could be involved in the development of the spontaneous mechanical tone observed in colon from dystrophic (mdx) mice. By recording the intraluminal pressure of isolated colon from normal mice, we showed that N(omega)-nitro- L-arginine methyl ester (L-NAME) increased the tone, even in the presence of tetrodotoxin. The effect was prevented by L-arginine, nifedipine, or Ca(2+)-free solution. In colon from mdx mice, L-NAME was ineffective. Immunohistochemistry revealed that the presence and distribution of neuronal (nNOS), endothelial, and inducible NOS isoforms in smooth muscle cells and neurons of colon from mdx mice were the same as in controls. However, the expression of myogenic nNOS was markedly reduced in mdx mice. We conclude that there is a myogenic NOS in mouse colon that can tonically produce nitric oxide to limit influx of Ca(2+) through L-type voltage-dependent channels and modulate the mechanical tone. This mechanism appears to be defective in mdx mice.

Functional role of inducible nitric oxide synthase on mouse colonic motility

A possible functional role of inducible isoform of nitric oxide synthase (iNOS) was explored in vitro on the motility of mouse distal colon. Using an isotonic - non-isovolumic technique, peristaltic activity and video images of the external wall of colonic segments were recorded before and after addition to the medium of Aminoguanidine (AG) and N-(3-(aminomethyl)benzyl) acetamidine (W1400) [10(-7) M-10(-4) M], two iNOS inhibitors. AG and W1400 induced an hyperexcitability of visceral smooth muscle characterised by an increase of basal tone and spontaneous phasic activity. As a consequence of these effects, the peristaltic activity declined and disappeared at the highest concentrations. These findings indicated a removal of inhibitory action performed by NO synthesised by iNOS in the colonic segment. The implications of results are discussed in term of tonic relaxation of intestinal smooth muscle to allow intraluminal content accommodation.

Increased calcium influx is responsible for the sustained mechanical tone in colon from dystrophic (mdx) mice

BACKGROUND & AIMS

Proximal colon from dystrophic mice develops spontaneous tone increment, but the mechanisms involved in its development have not been investigated. This study examined whether alterations in the properties of cell membrane calcium channels and/or sarcoplasmic reticular (SR) Ca2+-adenosine triphosphatase (ATPase) contribute to tone development.

METHODS

Effects of calcium-free solution, nifedipine, pinaverium (calcium channel blockers), and cyclopiazonic acid (CPA; SR Ca2+-ATPase inhibitor) on the contractile activity of colon from mdx and control mice were determined.

RESULTS

Calcium-free solution abolished spontaneous contractions in both preparations, but decreased the tone only in mdx mice. Nifedipine or pinaverium abolished phasic contractions, acting with different sensitivities on the 2 preparations. They also decreased the tone in colons of mdx mice, and Ca2+-free solution did not cause any further loss of tone. CPA, after an early contractile effect, abolished spontaneous contractions in control animals. It did not suppress the contractile activity in mdx mice. CPA inhibited the repletion of intracellular calcium stores in both tissues to the same degree.

CONCLUSIONS

Increased Ca2+ influx through L-type voltage-dependent Ca2+ channels seems to be responsible for the sustained mechanical tone of proximal colon from mdx mice. The mechanisms for sequestering calcium appear to be unaltered.

Altered electrical activity in colonic smooth muscle cells from dystrophic (mdx) mice

Because the colon from dystrophic (mdx) mice shows an altered motor pattern, probably due to neural disorders, our aim was to examine the electrophysiological properties of muscle cells and the functionality of nitrergic transmission in circular muscle from normal and mdx colon. Normal colonic cells (resting membrane potential [RMP] about -50 mV) showed spontaneous hyperpolarizations (inhibitory junction potentials; IJPs) and cyclic slow depolarizations were sometimes recorded. Mdx colon had a depolarized RMP (about -36 mV) and spontaneous IJPs, but the cyclic activity was never observed. In the normal colon, Nomega-nitro-L-arginine methyl ester (L-NAME) induced depolarization and abolished the cyclic activity. In the mdx colon, L-NAME caused a slight depolarization. Both preparations displayed the same value of RMP in the presence of L-NAME. In normals, neural stimulation induced nonadrenergic, noncholinergic IJPs composed of fast hyperpolarizations followed by a nitrergic slow hyperpolarization, selectively abolished by L-NAME. In the mdx colon the evoked IJPs were composed only of the initial fast hyperpolarization, the nitrergic component being absent. The hyperpolarization to sodium nitroprusside was not significantly different in both preparations. We conclude that the colon from animals lacking in dystrophin displays different electrophysiological features because of an impairment of nitric oxide function.

Spontaneous migrating motor complexes occur in both the terminal ileum and colon of the C57BL/6 mouse in vitro

We have studied migrating motor complexes (MMCs) in the isolated terminal ileum or colon (IMMCs and CMMCs respectively) of the C57BL/6 mouse. Periodic contractions occurred spontaneously in both preparations in the absence of intraluminal stimulation. After an initial period, complexes became synchronized between the oral and anal ends of the tissue, and could be observed for in excess of 7 h. The propagation velocity was 3.1+/-1.0 and 3.9+/-0.6 mm s(-1) in the ileum and colon respectively. IMMCs occurred every 6.01+/-0.39 min and had a duration of 86.3+/-10.4 s. The interval between CMMCs was smaller (3.52+/-0.31 min) and contractions were shorter in duration (30.7+/-3.6 s). In both preparations, these motor events were dependent on cholinergic transmission: blocked by hexamethonium (500 microM) and attenuated or blocked by atropine (1 microM). This study is the first demonstration of spontaneous migrating contractions in the isolated ileum or colon of the C57BL/6 mouse, the strain of choice for neurological transgenic and targeted mice.

Mechanical activity of small and large intestine in normal and mdx mice: a comparative analysis

The aim of this study was to compare the motor pattern (recorded as changes in intraluminal pressure) of isolated duodenum and proximal colon between dystrophic mdx and normal mice. When duodenal recordings from control preparations were compared with mdx mice there was no significant difference in the spontaneous motor pattern, responses to electrical nerve stimulation or sensitivity to pharmacological agents. Colonic segments from mdx mice showed a more complex motor pattern, consisting of contractions with amplitude and frequency similar to those of controls and by additional contractions with lower amplitude and higher frequency. Moreover, 70% of the colonic preparations from mdx mice developed active tone. TTX (1 microM), both in control and in mdx mice, changed the motor pattern, revealing regular rhythmic contractions similar in both preparations. L-NAME (100 microM) in both preparations increased contractile activity, revealing additional low contractions in control and potentiating them in mdx colon. In both control and mdx mice, inhibitory responses elicited by electrical field stimulation (EFS) were significantly attenuated by L-NAME. Our results provide evidence for the presence of a different motor pattern in mdx proximal colon and suggest that mdx mice can be considered a suitable animal model for investigating the dystrophic process.

Nitric oxide regenerates the normal colonic peristaltic activity in mdx dystrophic mouse

We demonstrated in vitro that the colonic peristaltic activity is modified in dystrophin-deficient mdx mouse indicating a defect in the enteric nervous system (ENS). Since nitric oxide (NO) has been proposed as a putative inhibitory mediator of ENS, here we have examined the effects of both L-Arginine (L-Arg) and Nomega-nitro-L-arginine methyl ester (L-NAME) on the peristaltic activity of mdx mouse distal colon. The motor pattern of colonic segment showed irregular peristaltic waves. L-Arg (10(-7) - 10(-5) M) induced the peristaltic activity to slow down. At a concentration of 10(-5) M, L-Arg produced hypomotility, characterised by a decrease in amplitude, frequency and ejected fluid volume. Conversely, L-NAME elicited hypermotility, this effect being reversed once again by the subsequent addition of L-Arg. Interestingly the addition of 10(-5) M L-Arg to the organ bath led to the normal progression, in an oral to aboral direction, of 90% of the peristaltic waves. This last result strongly suggests that exogenous application of L-Arg restores the integrative circuits of the ENS responsible for programming and co-ordinating peristaltic activity in the distal colon of mdx mouse.

In vitro excitatory actions of corticotropin-releasing factor on rat colonic motility

Corticotropin-releasing factor (CRF) has been shown to affect gastrointestinal functions, however, a direct effect of CRF on the intestine has not been demonstrated. To determine the direct effect of CRF and its antagonist alpha-helical-CRF9-41 (alpha-h-CRF) on the enteric nervous system, we studied the action of these substances on electrical and mechanical parameters of peristaltic activity on isolated distal colon of the rat. The effects of CRF were evaluated in vitro on rat isolated colonic segments in which intraluminal pressure, longitudinal displacement, ejected fluid volume and extracellular electrical activity were simultaneously recorded during colonic peristaltic reflex. The addition of CRF (10(-10) - 10(-8) M) to the bath fluid provoked a concentration-dependent increase of both mechanical and electrical peristaltic activity. The CRF-receptor antagonist alpha-h-CRF dose-dependently (10(-10) - 10(-7) M) induced a decrease of the colonic mechanical and electrical activity and prevented (10(-8) - 10(-6) M) CRF (10(-8) M) maximal effects. These results indicate: (a) CRF can exert its effects on colon functions by a direct action, (b) a specific CRF-receptor is present in the rat colon. Indeed, CRF effects are antagonized by the specific CRF antagonist alpha-h-CRF, (c) the fact the alpha-h-CRF displays an activity on its own reveals that colonic functions are controlled by an endogenous CRF tonic activity.